All direct injected engines, both gasoline and diesel, directly add fuel to the combustion chamber bypassing the intake valves for efficient combustion. Some of the exhaust and crankcase vapor gas is recirculated back to the air intake and over the intake valves. This can cause a buildup of a carbonaceous material on and around the manifold and air intake valves, which eventually decreases fuel efficiency and performance.
Some of this deposit can be removed by adding a cleaning composition into the air intake. Current cleaning compositions are generally organic solvent-based and therefore are suitable only for gasoline engines and are unsuitable for diesel engines. The fuel value of the solvents causes unintended increases in engine acceleration, sometimes resulting in damage from uncontrolled or run away combustion.